The radiolabelled 4P-PDOT will be used in receptor autoradiography to localize and quantify melatonin receptors in brain, retina, and vascular mammalian tissues. Activation of the MT2 melatonin receptor inhibits dopamine release in retina, phase shifts circadian rhythms in mice, and induces vasodilation in rat arteries. Although MT2 mRNA expression is found in the suprachiasmatic nucleus, cerebellum, hippocampus, retina, superior cervical ganglia, cerebral and peripheral arteries, there is no evidence for the presence of the protein using 2-[125I]-iodomelatonin. The availability of radiolabelled 4P-PDOT will further the field of melatonin receptor research. User Details: Experiment Details: User Number: 1705 Tritiation City, State: Menlo Park, CA HPLC Funding Source: NIH 3 N01 MH80015 NMR (PI: Jeanne S. Macino) 1 day Charge: $2067.47 1 compound Program Income: $2066.85